1. Field of the Invention
The present invention concerns a photoresist composition and a method of exposing the photoresist. The Photoresist has been utilized, for example, for forming a pattern of an electronic part such as a semiconductor device. The present invention can be utilized generally in various application uses of the photoresist and, in particular, it can be utilized suitably in a case of using the photoresist when focusing upon exposure is determined by measurement using infrared rays.
2. Description of the Prior Art
In the case of exposing the photoresist, focusing has been detected by using infrared rays. FIG. 2(a) shows an example of measuring a distance when a photoresist 2 is formed on a semiconductor substrate 1a by coating followed by exposure using an infrared light 31 as an auto-focusing light. As shown in FIG. 2(a), the infrared light 31 is reflected on the surface of the photoresist 2, and the distance is measured by the surface reflection light 32, thereby automatically detecting the focusing position.
However, an exposure device of using the infrared light for an auto-focusing detection system has involved a problem that infrared light transmits by about 100% in the photoresist layer 2 making it impossible to correctly detect the auto-focusing at the surface of the photoresist layer 2.
As shown in FIG. 2(a), in the prior art, incident infrared light 31 for the detection of auto-focusing transmits the photoresist 2 to form a transmission light 38, which causes reflection on the surface of the substrate 1a to form a secondary reflection light 34. The secondary reflection light is further reflected at the surface of the photoresist 2 into the photoresist 2 and, further, reflected on the surface of the substrate 1a to sometimes form a tertiary reflection light 35. As a result, in the prior art, the reflected infrared rays are incident into the auto-focusing detection system in the form having a certain width, which results in deterioration of detection accuracy in the auto-focusing detection system.
In a case where the underlying substrate is made of a material capable of transmitting infrared light, the problem becomes more significant. FIG. 2(b) shows an example of measuring a distance when a photoresist 2 is formed on a quartz glass substrate 1b. As shown in FIG. 2(b), since a quartz glass substrate is used as the substrate in for example a TFT (thin film transistor) process, a light 36 transmitting the quartz glass substrate 1b is also reflected at the rear face of the substrate 1b into a reflection light 37 and it then enters the detection system. Accordingly, the detection accuracy for auto-focusing is further worsened.
Generally, in the optical auto-focusing described above, the upper surface of a member to be exposed is detected, which is driven so as to be aligned with an image surface of a projection lens. In the detection for the position of the upper surface, the position is measured by reflecting the infrared light emitting from a light emitting diode or the like on the upper surface of the exposed member and by detecting the position of the reflection light by a position sensor (PSD). In this case, if different reflection lights 32, 34, 35, 37 are present as described above and the detection light at an optical intensity distribution with a width enter the detection system, the output of PSD (position measuring value) indicates the gravitational center of the light intensity distribution. Accordingly, it suffers from the effect due to the mixing of the reflection light other than the surface reflection light 32. It is possible to use infrared light of three wavelength as the detection light (for example, infrared light at a wavelength of 880, 800 and 730 nm), thereby offsetting the deviation due to interference to some extent but it is eventually insufficient. Furthermore, the detection light in autofocusing as described above also suffers from remarkable effect by the thickness of the substrate (substrate made of semiconductor, quartz glass or the like), the nature of the layer on the substrate (layer thickness, refractive index, reflectance), etc. Although it is ideal that the focus value does not fractuate even if the thickness of each of the films should vary, the effect of the layer thickness or the like is large in the existent technique.